Infants, between birth and six months of age, are tested on tasks involving complex auditory discriminations. The proposed research would investigate infants' ability to discriminate directionality of sounds in a free field acoustic environment using sounds from one loudspeaker, or from two loudspeakers located to the left and right of the subject. The latter sound stimulus would consist of one sound leading the other in time soas to give the perception of a single sound from a single source located on the side of the leading sound. This phenomenon, known as the precedence effect, appears to require cortical processing in order for the subject to perceive the two sounds as one in this situation, and is therefore a more difficult discrimination than required for a single source sound. A hierarchy of tasks are proposed, so that easy and difficult sensory discriminations are paired with a variety of responses ordered in difficulty. The tasks range from the use of heart rate change to detect a simple shift in direction from one side to the other, to tasks demanding identification of sound direction to predict or control external events in classical or operant conditioning.